Projection system and projector

ABSTRACT

A projection system includes: a relay system that focuses light having exited through a first image plane on a second image plane; and an enlarging system that enlarges and projects an image focused on the second image plane on a third image plane, wherein the relay system includes a first lens element on which the light having exited through the first image plane is incident, the first lens element having positive refracting power, a reflective member that reflects a light having passed through the first lens element, the reflective member having positive refracting power, and a second lens element on which a light reflected off the reflective member is incident and which focuses the light reflected off the reflective member on the second image plane, the second lens element having positive refracting power.

BACKGROUND

1. Technical Field

The present invention relates to a projection system and a projector.

2. Related Art

As an apparatus capable of displaying a large screen image, there hasbeen a commercially available projector in which light from a lightsource apparatus illuminates a small light modulator that forms anoptical image in accordance with image information and the optical imageis enlarged and displayed through a projection lens on a screen or anyother suitable surface.

In recent years, the performance of projectors has significantlyprogressed. Such high performance owes greatly to an optical system of aprojector. For example, an ultra-short focal length optical system and ahigh magnification optical zooming system allow a user to use aprojector more comfortably, and a rigorously designed optical systemsubstantially free of lens aberrations allows the resolution of an imageto be increased.

To incorporate more advanced features, it is more difficult to design anoptical system that satisfies the requirements. On the other hand,attempts to design an optical system having excellent performancequality tend to end up increase in size of the optical system. As aresult, the overall size of a projector increases, which is againstmarket requirements of reduction in size of a projector and hencecontributes to decrease in value for customers.

To address the problem, many studies have been conducted on reduction insize of an optical system (see JP-A-2005-157153, for example). InJP-A-2005-157153, a relay system disposed between an image displaydevice (panel) and a projection lens is used to form an intermediateimage magnified to be larger than the panel and located on the objectside (panel side) of the projection lens, whereby the f-number (an indexrepresenting the brightness expressed by the ratio of the focal lengthof a lens to the diameter of an entrance pupil) is increased. As aresult, the back focal length can be reduced, and an ultra-wide angleprojection lens is achieved.

The method described above, however, has the following problem: That is,when a relay system capable of displaying a high-definition image isrequired, a large number of lenses are used to design the opticalsystem, as described in JP-A-2005-157153, probably resulting in anincreased length of the overall optical system including the projectionlens. Further, an optical system is, in general, designed inconsideration of aberrations induced by the lenses used in the opticalsystem, and the design tends to be complicated when the number of lensesthat form the optical system increases. When an optical system inquestion is a telecentric relay system, the design is much morecomplicated.

SUMMARY

An advantage of some aspects of the invention is to provide a projectionsystem having a simple structure but capable of displaying ahigh-definition image. Another advantage of some aspects of theinvention is to provide a projector including the projection system.

A projection system according to an aspect of the invention includes arelay system that focuses light having exited through a first imageplane on a second image plane and an enlarging system that enlarges andprojects an image focused on the second image plane on a third imageplane. The relay system includes a first lens element on which the lighthaving exited through the first image plane is incident, the first lenselement having positive refracting power, a reflective member thatreflects a light having passed through the first lens element, thereflective member having positive refracting power, and a second lenselement on which a light reflected off the reflective member is incidentand which focuses the incident light reflected off the reflective memberon the second image plane, the second lens element having positiverefracting power.

According to the configuration described above, since the reflectivemember is used to fold the optical path, the overall length of the relaysystem can be set not to be long, but the configuration of the relaysystem can be compact. Further, the reflective member does not producecolor aberrations. Providing the relay system described above allows theprojection system to be compact and free of color aberrations.

In the aspect of the invention, a principal ray of a light that isincident on the first lens element is desirably parallel to a principalray of a light that exits through the second lens element.

According to the configuration described above, when other opticalsystems are disposed upstream and downstream of the projection system,assembly and adjustment thereof is readily carried out because thedirections of the principal rays of the incident and exiting light arealigned.

In the aspect of the invention, the projection system desirably furtherincludes a first reflection mirror that not only reflects the lighthaving passed through the first lens element such that the light havingpassed through the first lens element is guided to the reflective memberbut also reflects a light reflected off the reflective member such thatthe light reflected off the reflective member is guided to the secondlens element.

According to the configuration described above, since the optical pathis further deflected in the relay system, the overall projection systemcan have a compact configuration.

In the aspect of the invention, the projection system desirably furtherincludes a second reflection mirror that reflects a light having passedthrough the second lens element.

According to the configuration described above, since the degree offreedom in setting the position where the second image plane is formedincreases, a downstream optical system is readily connected to the relaysystem while preventing interference with other members from occurring.As a result, the projection system can have a high degree of freedom interms of position where it is located.

In the aspect of the invention, a shape of the first lens element is thesame as a shape of the second lens element, and a refractive index ofthe first lens element is the same as a refractive index of the secondlens element.

According to the configuration described above, since a single commonlens element can be used, the number of members to be prepared can bereduced.

In the aspect of the invention, it is desirable that the reflectivemember has a plane-symmetrical shape that is symmetric with respect to asymmetry plane including the optical axis of the reflective member, andthat the first lens element and the second lens element are disposed tobe symmetric with respect to the symmetry plane.

According to the configuration described above, since the lens elementsare disposed to be symmetric with respect to the symmetry plane, a lightray having exited through the first lens element readily incident on theposition on the second lens element that corresponds to the position onthe first lens element through which the light ray has exited, wherebycolor aberrations can be canceled in a satisfactory manner.

In the aspect of the invention, it is desirable that the first lenselement and the second lens element constitute a single lens memberhaving positive refracting power. It is also desirable that the lensmember has a shape rotationally symmetric around an optical axisthereof, and that the reflective member has a shape rotationallysymmetric around the optical axis of the lens member.

According to the configuration described above, since the first lenselement and the second lens element constitute a single lens member, alight ray having exited through the first lens element readily incidenton the position on the second lens element that corresponds to theposition on the first lens element through which the light ray hasexited, whereby color aberrations are canceled in a satisfactory manner.Further, since the symmetry axis of the lens member coincides with thesymmetry axis of the reflective member, the members are readily alignedwith each other. Moreover, since the number of components is reduced,the configuration of the projection system can be simplified, andassembly and adjustment thereof can be readily carried out.

In the aspect of the invention, the light incident on the first lenselement desirably travels in a telecentric manner.

According to the configuration described above, the shape of the imagein the second image plane does not change even when the first imageplane is slightly inclined with respect to the optical axis of the firstlens element, whereby the projection system acts in a satisfactorymanner.

In the aspect of the invention, it is desirable that a light havingexited through the second lens element travels in a telecentric manner,and that the second image plane is inclined to the first image plane.

In the relay system in the projection system according to the firstaspect of the present application, it is required to fabricate the lenselement with high accuracy considering the aberrations induced by thelens element, when telecentricity of the light having exited through thesecond lens element is desired. Further, it is required to fabricate thelens element with higher accuracy in order to locate the first imageplane and the second image plane in the same plane. In this case, theconfiguration of the projection system may not be simple. To address theproblems, in the projection system according to the aspect of theinvention, the first image plane and the second image plane are inclinedto each other so that the advantageous effect of the invention isachieved without complicated fabrication of the lens element.

In the aspect of the invention, the projection system desirably furtherincludes a light level adjusting member disposed in an optical pathbetween the first lens element and the reflective member, the lightlevel adjusting member limiting the amount of light incident on thereflective member.

According to the configuration described above, the light having exitedfrom the first image plane can be uniformly limited.

In the aspect of the invention, the projection system desirably furtherincludes a first optical member which is disposed between the firstimage plane and the first lens element and through which the lighthaving exited from the first image plane passes and a second opticalmember disposed between the second lens element and the second imageplane, the second optical member allowing an optical distance between asurface of the second lens element through which light exits and thesecond image plane to be equal to an optical distance between the firstimage plane and the first lens element.

According to the configuration described above, the optical distancefrom the first image plane to the first lens element is equal to theoptical distance from the surface of the second lens element throughwhich light exits to the second image plane, for example, even when adichroic prism or any other light transmissive member is used as thefirst optical member. Consequently, aberrations induced by the opticalmember are canceled by the second optical member, and hence distortionand color aberrations can be suppressed.

In the aspect of the invention, a refractive index of the first opticalmember is desirably equal to a refractive index of the second opticalmember.

According to the configuration described above, the optical distancefrom the first image plane to the first lens element can readily beaccurately equal to the optical distance from the surface of the secondlens element through which light exits to the second image plane in anaccurate manner, whereby distortion and color aberrations can besuppressed.

In the aspect of the invention, the second optical member desirably hasa reflection layer that reflects the light having passed through thesecond lens element.

According to the configuration described above, the projector can have ahigh degree of freedom in positioning the components.

A projector according to another aspect of the invention includes alight source, a light modulator which is provided in the first imageplane and on which light emitted from the light source is incident, andthe projection system described above.

According to the configuration described above, the projector can have ashort back focal length and display a high-quality image.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a diagrammatic view showing a schematic configuration of aprojector according to an embodiment of the invention.

FIG. 2 describes the configuration of a projection system according tothe embodiment of the invention.

FIG. 3 describes the configuration of another projection systemaccording to the embodiment of the invention.

FIG. 4 describes the configuration of another projection systemaccording to the embodiment of the invention.

FIG. 5 describes the configuration of another projection systemaccording to the embodiment of the invention.

FIG. 6 describes the configuration of another projection systemaccording to the embodiment of the invention.

FIG. 7 describes the configuration of another projection systemaccording to the embodiment of the invention.

FIG. 8 describes the configuration of another projection systemaccording to the embodiment of the invention.

FIG. 9 describes the configuration of a projection system according toanother embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Projection systems and projectors according to embodiments of theinvention will be described below with reference to FIGS. 1 to 9. In thefollowing drawings, the dimensions, aspect ratios, and other factors ofcomponents are not to scale as appropriate for ease of illustration.

Projector

FIG. 1 is a diagrammatic view showing a schematic configuration of aprojector PJ including a projection system according to an embodiment ofthe invention. As shown in FIG. 1, the projector PJ includes anillumination system (light source) 10, a color separation system 20,liquid crystal light valves (light modulators) 30 a to 30 c, a lightcombining system 40, a relay system 50, and an enlarging system 60. Therelay system 50 and the enlarging system 60 together form a projectionsystem 70.

The projector PJ generally operates as follows: Light L emitted from theillumination system 10 is incident on dichroic mirrors 21 and 22included in the color separation system 20 and divided into red lightLa, green light Lb, and blue light Lc, which then travel via mirrors 23,24, and 25 and lenses 26 a to 26 c, 27, and 28 and are incident on andmodulated by the respective liquid crystal light valves 30 a to 30 c.

The plurality of color light fluxes modulated by the liquid crystallight valves 30 a to 30 c are incident on a dichroic prism 40 andcombined therein. The light combined in the dichroic prism (firstoptical member) 40 is enlarged and projected through the projectionsystem 70 on a projection surface (third image plane) 80, such as a wallor a screen. A full-color projected image is thus displayed.

Projection System

The projection system 70 according to the embodiment of the invention isreduced in size by using a reflective member in the relay system 50 asdescribed below, and the overall length of the projection system 70 isnot long. Examples of the relay system 50 included in the projectionsystem 70 will be described in order with reference to FIGS. 2 to 8, andthe projection system 70 in the present application including the relaysystem will then be described.

FIG. 2 describes a basic configuration of the relay system 50 in theprojection system according to the embodiment of the invention. A relaysystem 50A shown in FIG. 2 includes a lens member 51 and a concavemirror (reflective member) 52. Each of the lens member 51 and theconcave mirror 52 has a shape axially symmetric around a rotational axis50L, that is, the rotational axes of the lens member 51 and the concavemirror 52 coincide with each other.

The lens member 51 is a plano-convex lens having a curved surface facingthe concave mirror 52. The lens member 51 is fixed by using a holder 59in an appropriate position. The lens member 51 is divided with a planeincluding the rotational axis 50L into a first lens element 51 adisposed on one side and a second lens element 51 b disposed on theother side, and a direction in which light passes through the first lenselement is opposite to a direction in which light passes through thesecond lens element. In other words, the first lens element and thesecond lens element 51 a, 51 b are disposed symmetrically with respectto the plane including the rotational axis 50L. Further, the lightincident on the first lens element 51 a and the light incident on thesecond lens element 51 b have principal rays parallel to each other.

The state in which “principal rays are parallel to each other” in theinvention conceptually includes a state in which they are slightly outof parallelism due to aberrations induced by the lens member 51.

The concave mirror 52 has a curved surface facing the lens member 51 andreflects the light having passed through the lens member 51 back towardthe lens member 51. In detail, the concave mirror 52 reflects a lightray having exited through the first lens element 51 a and directs thereflected light to a position on the second lens element 51 b thatcorresponds to the position on the first lens element 51 a through whichthe light ray has exited. “The position on the second lens element 51 bthat corresponds to the position on the first lens element 51 a throughwhich the light ray has exited” used herein is the position on thesecond lens element 51 b that is symmetric to the corresponding positionon the first lens element 51 a with respect to the plane including therotational axis 50L, which divides the lens member 51 into the firstlens element and the second lens element 51 a, 51 b.

A diaphragm (light level adjusting member) 58 for adjusting the amountof light may be provided in the vicinity of the surface of the concavemirror 52 on which light is incident. The diaphragm 58 can be adiaphragm that mechanically controls the amount of light, such as alight-blocking plate, or a diaphragm that electrically controls theamount of light, such as a liquid crystal device. Providing thediaphragm 58 in this position allows the light having exited from afirst image plane S1 to be uniformly limited. The diaphragm 58 employedin the relay system 50A of the present embodiment adjusts its aperturesize by mechanically driving a light-blocking plate. In thisconfiguration, a displayed bright image can be brighter by opening thediaphragm 58, whereas a displayed dark image can be darker by closingthe diaphragm 58. In this way, an image can be displayed with anappropriate amount of light according to the grayscales of the image,whereby an image having a wide dynamic range can be displayed.

In the thus configured relay system 50A, the light having exited fromthe first image plane S1 passes through the first lens element 51 a andimpinges on the concave mirror 52. The light reflected off the concavemirror 52 then passes through the second lens element 51 b and isfocused on a second image plane S2. In the projector PJ shown in FIG. 1,one of the liquid crystal light valves is disposed in the position ofthe first image plane S1, and the dichroic prism 40 is disposed betweenthe first image plane S1 and the first lens element 51 a in a positionfacing the first lens element 51 a.

In the relay system 50A, when light passes through the first lenselement 51 a, the light is degraded by color aberrations, but when thelight passes through the second lens element 51 b, the color aberrationsare canceled. On the other hand, no color aberration is produced by theconcave mirror 52. Consequently, color aberrations can be suppressed inthe relay system 50A.

In the relay system 50A, since the optical path is folded by the concavemirror 52, the overall length of the relay system 50A is not long buthas a compact configuration. Further, to achieve a bilateral telecentricrelay system, in general, it is necessary to employ a configuration inwhich a large number of lenses are combined, as described inJP-A-2005-157153. However, since the relay system 50A is primarilyformed of the lens member 51 and the concave mirror 52, a bilateraltelecentric relay system is achieved by using a smaller number ofcomponents.

The projection system according to the embodiment of the inventionincluding the relay system 50A described above can be reduced in size,and color aberrations can be suppressed.

A variety of components can be added to the basic configuration of therelay system of the present embodiment shown in FIG. 2.

For example, in a relay system 50B shown in FIG. 3, a reflection mirror(second reflection mirror) 53 that reflects the light having passedthrough the second lens element 51 b may be disposed in a positionfacing the second lens element 51 b to change the direction in which theexiting light travels so that the position of the second image plane S2is changed. The thus configured relay system can have a high degree offreedom in terms of position where it is located. Specifically, one ofthe liquid crystal light valves is readily disposed in a position facinga surface 40 a of the dichroic prism 40.

Further, in a relay system 50C in shown FIG. 4, a dummy prism (secondoptical member) 54 having the same shape as that of the dichroic prism40 and made of a material having the same refractive index as that ofthe dichroic prism 40 may be disposed in a position facing the secondlens element 51 b. The configuration described above allows the opticaldistance from the first image plane S1 to the first lens element 51 a tobe equal to the optical distance from the surface of the second lenselement 51 b through which light exits to the second image plane S2,whereby aberrations induced in the dichroic prism 40 are canceled in thedummy prism 54 and hence distortion and color aberrations can besuppressed.

Further, in a relay system 50D shown in FIG. 5, a triangular prism 55having a reflection layer 55 a may be disposed in a position facing thesecond lens element 51 b. It is preferable that the triangular prism 55is made of a material having the same refractive index as that of thedichroic prism 40 and has the same geometric length of the optical pathas that of the light passing through the dichroic prism 40. The thusconfigured relay system 50D allows distortion and color aberrations tobe suppressed, as in the relay system 50C, and can have a high degree offreedom in terms of position where it is located, as in the relay system50B.

Further, in a relay system 50E shown in FIG. 6, a reflection mirror(first reflection mirror) 56 may be disposed between the lens member 51and the concave mirror 52. In the relay system 50E, the optical path ofthe light having exited through the lens member 51 is deflected by thereflection mirror 56 approximately by 45 degrees. The concave mirror 52,on which the light reflected off the reflection mirror 56 is incident,is disposed on the same side of the optical path connecting the lensmember 51 to the reflection mirror 56 as where the projection lens 60 isdisposed, and the light guided from the reflection mirror 56 to theconcave mirror 52 is reflected not only in the same direction in whichthe light having exited through the projection lens 60 travels but alsoin the direction parallel thereto.

That is, it is possible to prevent the distance between the lens member51 and the concave mirror 52 from being so long by using the reflectionmirror 56 to reflect the light having exited through the lens member 51.Further, the components that form the projection system 70 are disposednot to spread two-dimensionally by disposing the concave mirror 52 andthe projection lens 60 close to each other.

The entire projection system 70 including the thus configured relaysystem can be further reduced in size.

The thus configured projection system, in which the reflective member isused to deflect the optical path so that the size of the relay system isreduced, can be compact. In addition, color aberrations can besuppressed in the thus configured projection system.

In the projector including the projection system described above, theapparatus configuration can be compact, and a high-quality image withsuppressed color aberrations can be displayed. Further, the problem of along back focal length can be solved. Consequently, the optical systemof the projector has an ultra-short focal length and allows anultra-high-definition image to be displayed.

In the present embodiment, each of the first lens element 51 a and thesecond lens element 51 b is part of the single lens member 51. The lenselements can alternatively be separate elements.

When the first lens element 51 a and the second lens element 51 b areseparated each other, they may have the same shape and the samerefractive index, as if the lens member 51 were divided with a planeincluding the optical axis thereof. Alternatively, the lens elementsmay, for example, be made of materials having different refractiveindices each other as long as the resultant lens elements provide thesame refracting power by separately designing their curvatures so thatthey have difference shapes each other.

When the first lens element 51 a and the second lens element 51 b areseparate elements as described above, the principal optical axis of thelight that is incident on the first lens element 51 a may not beparallel to the principal optical axis of the light that exits throughthe second lens element 51 b.

In the present embodiment, the lens member 51 of the relay system is aplano-convex lens having a curved surface facing the concave mirror 52.When the thus configured lens is used, the light that is incident on thefirst lens element 51 a can be telecentric, whereas the light that exitsthrough the second lens element 51 b may not be exactly telecentric dueto aberrations induced thereby in some cases. When the light that exitsthrough the second lens element 51 b should be exactly telecentric, theprojection system may include a lens member 57 designed to outputexactly telecentric light, for example, a relay system 50F shown in FIG.7.

In this case, the second image plane S2 may be inclined to the firstimage plane S1 by an angle θ, as shown in FIG. 8. Providing ahigh-performance bilateral telecentric relay system allows adjustment ofpositioning a lens (projection lens, for example) in the second imageplane S2 to be less difficult.

The inclination angle θ of the second image plane S2 may be canceled,for example, by employing a projection system including the reflectionmirror 53, which reflects light so that an image is projected on thethird image plane after the inclination is canceled.

The preferred embodiment according to the invention has been describedwith reference to the accompanying drawings, but the invention is, ofcourse, not limited thereto. The shapes, combinations, and other factorsof the components shown in the embodiment described above have beenpresented by way of example, and a variety of changes can be made basedon design requirements and other factors to the extent that the changesdo not depart from the substance of the invention.

For example, the above embodiment has been described with reference to aprojector including a projection system. The invention is alsoapplicable to a reduction optical apparatus because the optical path ofan optical member can generally be reversed, that is, the optical pathof the projection system can be reversed.

FIG. 9 is a schematic view showing a camera (imaging apparatus) 100,which is another optical apparatus using the optical system according tothe embodiment of the invention. In FIG. 9, the camera 100 includes therelay system 50A shown in FIG. 2. In the camera 100 shown in FIG. 9, animage of an object (third image plane, not shown) which is imaged on thesecond image plane S2 through a lens 101 is imaged on the first imageplane S1 through the relay system 50A and captured by an imager 102,which is a CCD sensor, CMOS sensor, or any other photoelectricconversion device disposed in the first image plane S1.

In the thus configured camera 100, since the relay system 50A is reducedin size, the apparatus configuration can be compact, and a capturedimage is a high-quality image with suppressed color aberrations.

Further, in a lens interchangeable camera, in which dirt, dust, andother unwanted objects on the imager greatly affect an image, theinfluence of these unwanted objects can be reduced because the firstimage plane is an aerial image plane. Moreover, since the back focallength is theoretically zero, any lens model can be attached as long asthe size of an image is the same.

The entire disclosure of Japanese Patent Application No. 2010-000101,filed Jan. 4, 2010 is expressly incorporated by reference herein.

1. A projection system comprising: a relay system that focuses lighthaving exited through a first image plane on a second image plane; andan enlarging system that enlarges and projects an image focused on thesecond image plane on a third image plane, wherein the relay systemincludes a first lens element on which the light having exited throughthe first image plane is incident, the first lens element havingpositive refracting power, a reflective member that reflects a lighthaving passed through the first lens element, the reflective memberhaving positive refracting power, and a second lens element on which alight reflected off the reflective member is incident and which focusesthe light reflected off the reflective member on the second image plane,the second lens element having positive refracting power.
 2. Theprojection system according to claim 1, wherein a principal ray of alight that is incident on the first lens element is parallel to aprincipal ray of a light that exits through the second lens element. 3.The projection system according to claim 1, further comprising a firstreflection mirror that not only reflects the light having passed throughthe first lens element such that the light having passed through thefirst lens element is guided to the reflective member but also reflectsa light reflected off the reflective member such that the lightreflected off the reflective member is guided to the second lenselement.
 4. The projection system according to claim 1, furthercomprising a second reflection mirror that reflects a light havingpassed through the second lens element.
 5. The projection systemaccording to claim 1, wherein a shape of the first lens element is thesame as a shape of the second lens element, and a refractive index ofthe first lens element is the same as a refractive index of the secondlens element.
 6. The projection system according to claim 5, wherein thereflective member has a plane-symmetrical shape that is symmetric withrespect to a symmetry plane including the optical axis of the reflectivemember, and the first lens element and the second lens element aredisposed to be symmetric with respect to the symmetry plane.
 7. Theprojection system according to claim 6, wherein the first lens elementand the second lens element constitute a single lens member havingpositive refracting power, the lens member has a shape rotationallysymmetric around an optical axis thereof, and the reflective member hasa shape rotationally symmetric around the optical axis of the lensmember.
 8. The projection system according to claim 1, wherein the lightincident on the first lens element travels in a telecentric manner. 9.The projection system according to claim 1, wherein a light havingexited through the second lens element travels in a telecentric manner,and the second image plane is inclined to the first image plane.
 10. Theprojection system according to claim 1, further comprising a light leveladjusting member disposed in an optical path between the first lenselement and the reflective member, the light level adjusting memberlimiting the amount of light incident on the reflective member.
 11. Theprojection system according to claim 1, further comprising: a firstoptical member which is disposed between the first image plane and thefirst lens element and through which the light having exited from thefirst image plane passes, and a second optical member disposed betweenthe second lens element and the second image plane, the second opticalmember allowing an optical distance between a surface of the second lenselement through which light exits and the second image plane to be equalto an optical distance between the first image plane and the first lenselement.
 12. The projection system according to claim 11, wherein arefractive index of the first optical member is equal to a refractiveindex of the second optical member.
 13. The projection system accordingto claim 11, wherein the second optical member has a reflection layerthat reflects the light having passed through the second lens element.14. A projector comprising: a light source; a light modulator which isprovided in the first image plane and on which light emitted from thelight source is incident; and the projection system according to claim1.